The present invention relates to machine tools, especially a hand-held power tool having a turnable clamping element for clamping a tool on the tool spindle. Such machine tools are known in the art and, for instance, disclosed in the German Auslegeschrifts Nos. 11 03 181 and 11 03 804. The tools used in these machine tools are clamped on the tool spindle by means of a usually hand-operated key, so as to clamp a for instance disk-shaped tool by means of a clamping nut and a clamping flange. For clamping a special key is necessary in certain cases also a tool for holding the tool spindle stationary during the clamping of the tool thereon. Such tools for clamping the tool on the tool spindle, which are used only occasionally, can get lost, or at least they are quite often not available when their use becomes necessary.